A gas turbine with a measuring arrangement for recording the temperature of a gas which flows in a passage which is circular in cross section, is known from GB 2 293 923 A. For this purpose, a plurality of thermocouples, which are distributed over the circumference of the passage, are installed in the passage wall. In order to protect their electrical instrument leads against the temperatures which prevail outside the passage, these are laid in a hermetically sealed protective environment which is formed from a system of interconnected tubes and branch boxes of stainless steel or aluminum.
At the terminating or connecting points of the tubes to the branch boxes, however, leakages can occur owing to thermal expansions, as a result of which hot ambient air can penetrate into the protective environment, and the insulation of the instrument leads can be subjected to unacceptably high temperatures. This can lead to erroneous measuring results, to defects on the insulation of the instrument leads, or even to the total failure of a probe.
A further disadvantage is the costly construction of tube-like protective sheaths and their sealed connections to the branch boxes in order to form a hermetic protective environment.
Furthermore, a cooled pyrometer for temperature measuring of a combustion hot gas is known from U.S. Pat. No. 5,348,395. The pyrometer comprises a double-sheathed thermoelement which is coolable in the interspace by water. A further cooled probe is known, for example, from U.S. Pat. No. 6,325,535.